asterisk users - Oct 2006 - fully featured and robust * client gui?

Hi,

My users are currently using a console interface like this:
see it at: http://www.whssf.org/interface.jpg

which came with a Praxon PDX we got about 5 years ago, which is now  
unsupported,
it works very good and converts any analog phone plugged into the  
system into a powerful console,
(provided you have a computer next to it)
you just provide the box ip, user login, user pass, and extension,  
and voila.

I'll be switching the company's phone system to Asterisk.

I know * is way much more flexible and rich featured than the box we  
currently have,

...but I'll need to give the users a good mean to "see"
what's going on,
who is busy,
easy transfer with click here and there,
easy conference,
easy queue handler,
easy way to see/use many lines at the same time

is there any "best" gui?

I don't mind using a commercial product,
if the only part we have to pay for is the gui,
besides, we will buying the enterprise * version

Thanks a bunch,

Andres